ENH1253

Biology and Management of Oxalis (Oxalis stricta) in Ornamental Crop Production1

Matt Lollar and Chris Marble2

1. This document is ENH1253, one of a series of the Environmental Horticulture Department, UF/IFAS Extension. Original publication date February 2015. Visit the EDIS website at http://edis.ifas.ufl.edu.

2. Matthew Lollar, commercial horticulture production Extension agent, Seminole County, Sanford, Florida; Chris Marble, assistant professor, Mid-Florida REC, Apopka, Florida;.UF/IFAS Extension, Gainesville, FL 32611.

Mention of a commercial or herbicide brand name or chemical does not constitute a recommendation or warranty of the product by the authors or the University of Florida, Institute of Food and Agricultural Sciences, nor does it imply its approval to the exclusion of other products that may also be suitable. Products should be used according to label instructions and safety equipment required on the label and by federal or state law should be employed. Pesticide registrations may change, so it is the responsibility of the user to ascertain if a pesticide is registered by the appropriate state and federal agencies for its intended use.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension office. U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.

Species DescriptionClass: Dicotyledonous plant.

Family: Oxalidaceae (wood sorrel family).

Other Common Names: Yellow woodsorrel, yellow oxalis, upright yellow sorrel, shamrock, lucky clover, good luck plant.

Life Span: Cool-season (spring and fall) perennial that persist year-round in warmer climates, annual in cooler climates.

Habitat: Often found in woodlands, grasslands, turf, disturbed sites, and drain holes of containers or on container media surface (Figure 1). Found in full-sun and partial-sun areas.

Distribution: Oxalis is believed to be native to North America and is found in most of the eastern and central United States and is also present in Europe, Africa, Asia, Japan, and New Zealand.

Growth Habit: Usually erect (upright) and readily branch-ing, but may also grow more prostrate (along soil surface).

Figure 1. Oxalis growing in loropetalum liner. Credits: Chris Marble, University of Florida, Mid-Florida REC.

2Biology and Management of oxalis (Oxalis stricta) in Ornamental Crop Production

Often forms dense mats from rhizomes (horizontal un-derground stems that form lateral shoots and adventitious roots) (Figure 2).

Seedling: Cotyledons often have a pink tint with alternate, trifoliate leaves with thin, heart-shaped leaflets that are creased in the middle (Figure 3). Leaflets are smooth on the upper surface and have minimal pubescence (hair) on the lower surfaces and margins.

Shoot: Stems are light green in color and slightly pubescent (hairy). Leaves are palmately compound, alternate, and light green, with entire (smooth) cordate (heart-shaped) leaflets that are 0.2 to 0.4 inches long and 0.2 to 0.4 inches wide.

Roots: Taprooted. Rhizomes form secondary fibrous root structure.

Inflorescence: Three flower stalks branch from a single main stalk, which arises from the leaf axils. Flowers are yellow, roughly 0.5 inches in diameter, and have 5 petals.

Flowers from spring through fall (Figure 4).

Fruit and Seeds: Capsule fruit, resembling the shape of okra pods, contain five ridges and are approximately 0.5 inches in length (Figure 5). Fruit are produced spring through fall. Seeds are flat, brown, and have a teardrop shape. Mature seed capsules explosively dehisce (expel) when touched.

Similar Species: Several oxalis species are common weed pests in ornamental plant production. Creeping woodsorrel (Oxalis corniculata) is a similar species that grows more prostrate, often has darker green to purplish leaves, and produces stolons (aboveground plant stem that roots at nodes) (Hall, Vandiver, and Sellers 2012). O. corniculata has more pubescent foliage, especially along leaf margins. Florida yellow woodsorrel (O. florida) closely resembles O. stricta but has slender stems, larger leaves, and a smooth to slightly hairy seed capsule (Unruh et al. 2013). Cuban

Figure 2. Mature oxalis growing in a nursery container.Credits: Chris Marble, University of Florida, Mid-Florida REC.

Figure 3. Oxalis seedling. Note heart-shaped leaflets and pinkish hue.Credits: Annette Chandler. University of Florida, Mid-Florida REC.

Figure 4. Oxalis flower.Credits: Annette Chandler. University of Florida, Mid-Florida REC.

3Biology and Management of oxalis (Oxalis stricta) in Ornamental Crop Production

purple woodsorrel (O. intermedia) and pink sorrel (Oxalis debilis var. corymbosa) have larger leaves, purple flowers, and reproduce by bulbs and seed. Various Oxalis species are available commercially as ornamentals, including a vast assortment of Oxalis purpurea cultivars that have large, pink, showy flowers. Trifolium spp. (clovers) have similarly shaped leaves but have ball-like clusters of flowers and belong to a completely different plant family.

Plant BiologyOxalis grows throughout the year in Florida (Neal and Derr 2005). Oxalis prefers moist soil but can grow in dry areas and in a variety of different soil types (Halvorson and Guertin 2003). Persistence in ornamental production and landscapes is due to its prolific seed production; a single plant may produce up to 5,000 seeds in a year. At maturity, seeds are dispersed from explosively dehiscent capsules up to 16 feet away from the parent plant and germinate quickly (Halvorson and Guertin 2003; Neal and Derr 2005). Newly developed seeds have been shown to have close to 100 percent germination soon after dispersal (Holt and Elmore 1985). Seeds require light to germinate and most germination occurs within a temperature range of 50°F to 84°F; however, seeds produced during warmer months have a broader germination temperature range than seeds produced during cooler months (Holt and Elmore 1985). Vegetative reproduction is prevalent in established popula-tions from axillary buds at nodes located on rhizomes (Halvorson and Guertin 2003). Oxalis can be found grow-ing in sidewalk cracks, alongside trails, in lawns, flower

beds, cultivated fields, and in container nursery stock in a wide range of elevations (Halvorson and Guertin 2003). In greenhouse studies, oxalis populations have been shown to negatively impact the growth rates of ornamental crops (Neal and Derr 2005).

ManagementPhysical and Cultural Control: Oxalis is most successfully controlled through hand weed-ing when plants are young (6 weeks or younger) and before seed capsules develop (Halvorson and Guertin 2003). It is nearly impossible to completely remove oxalis rhizomes and stolons once established in nursery containers (Neal and Derr 2005). Hand weeding should occur when soil is moist to avoid dislodging small ornamentals and to ensure that all vegetative portions (roots, rhizomes, etc.) are removed (Halvorson and Guertin 2003). Hand-pulled plants need to be removed from the field because any seeds left behind can continue to germinate. Shallow mulching can aid in suppressing germination by blocking seedling exposure to light (Holt and Elmore 1985). Oxalis is gener-ally tolerant of mowing and can develop a more prostrate growth habit in areas that are repeatedly mowed (Halvorson and Guertin 2003). Rototilling mature oxalis can promote the initiation of new plants by spreading cut rhizomes and stems (Halvorson and Guertin 2003). Sanitation is the most effective method for oxalis control in nurseries and greenhouses (Neal and Derr 2005). Regularly scout for this weed and check all incoming plants and liners for presence of oxalis before placing them in production beds.

Chemical Control:PREEMERGENCEOxalis is controlled with most preemergent herbicides labeled for nursery and landscape use. Preemergence herbicides will not work if stolons, rhizomes, or root and stem fragments are left behind after hand weeding. Con-tainers and planting beds need to be weed free at the time of application for preemergence herbicides to be effective. However, indaziflam (Marengo®, OHP, Inc.) can provide control of very small oxalis soon after it germinates, up to the four-leaf stage (Marble et al. 2013). Marengo® should be applied as a directed application. A partial list of preemer-gence herbicides labeled for use in and around ornamentals that provide control of oxalis is given in Table 1.

POSTEMERGENCEThere are many different postemergence herbicides that are effective for oxalis control but most have to be applied as a directed application. Effective active ingredients

Figure 5. Oxalis seed pods. Seed are forcibly expelled when mature.Credits: Annette Chandler. University of Florida, Mid-Florida REC.

4Biology and Management of oxalis (Oxalis stricta) in Ornamental Crop Production

include glyphosate (RoundUp®), glufosinate (Finale®), diquat (Reward®), and pelargonic acid (Scythe®), among several others. Both systemic and contact herbicides will provide effective control, but thorough coverage is needed for contact herbicides such as diquat or pelargonic acid. Postemergence herbicides are most effective when the weeds are small and actively growing. Always consult the manufacturer’s label and follow all precautions when applying herbicides.

ReferencesHall, D. W., V. V. Vandiver, and B. A. Sellers. 2012. “Creep-ing Wood Sorrel, Oxalis corniculata L. Southern Yellow Wood Sorrel, Oxalis florida Salisb.” SP37. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences.

Halvorson, W. L. and P. Guertin. 2003. “Factsheet for: Oxalis stricta L.” USGS Weeds in the West project: Status of Introduced Plants in Southern Arizona Parks. Tucson, Arizona.

Holt, J. and C. Elmore. 1985. “Oxalis—Biology and Con-trol.” Ornamentals Northwest Archives 9(2):6–8.

Mallory-Smith, C. A. and E. J. Retzinger Jr. 2003. “Revised Classification of Herbicides by Site of Action for Weed Resistance Management Strategies.” WeedTech 17:605-619.

Marble, S. C., C. H. Gilliam, G. R. Wehtje, and M. Samuel-Foo. 2013. “Early Postemergence Control of Yellow Woodsorrel (Oxalis stricta L.) with Residual Herbicides.” WeedTech 27:347–351.

Murphy, T. R. 2007. Weeds of Southern Turfgrasses. SP079. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences.

Neal, J. C. and J. F. Derr. 2005. Weeds of Container Nurseries in the United States. Raleigh, NC: North Carolina Associa-tion of Nurserymen, Inc.

Unruh, J. B., D. E. P. Telenko, B. J. Brecke, and R. Leon. 2013. “Yellow Woodsorrel (Oxalis) Biology and Manage-ment in Turf.” ENH1124. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences.

5Biology and Management of oxalis (Oxalis stricta) in Ornamental Crop Production

Table 1. Preemergence herbicides labeled for use in ornamental plant production and landscapes to control yellow woodsorrel (oxalis).

Common Name (active ingredient)

Example trade name and

formulation

WSSA Herbicide

Group1

Efficacy2 Container production

Field production

Greenhouse or fully enclosed

structures

Landscape

dithiopyr Dimension® 2EW 3 C YES YES NO YES

oryzalin Surflan® 4AS 3 YES YES NO YES

Oryzalin 4 Pro 3 C YES YES NO YES

pendimethalin Pendulum® 2G 3 S-C YES YES NO YES

Pendulum® 3.3EC, 3.8AC

YES YES NO YES

prodiamine Barricade® 4FL, 65 WG

3 S-C YES YES NO YES

trifluralin Treflan 5G 3 S YES YES NO YES

simizine Simizine 4L 5 P-S YES YES NO YES

flumioxazin Broadstar™ 0.25G 14 C YES YES NO YES

SureGuard® 51WDG

YES3 YES3 NO YES4

oxadiazon Ronstar® 2G 14 C YES YES NO YES

oxyfluorfen Goal® 2XL (EC) 14 C YES3 YES3 NO NO

dimethenamid-p Tower® 6EC 15 C YES YES NO YES

s-metolachlor Pennant Magnum® 7.6 EC

15 P-S YES YES NO YES

dichlobenil Casoron® 4G 20 C NO YES NO YES

isoxaben Gallery® 75DF, 4.16SC

21 C YES YES NO YES

indaziflam Marengo® 0.622 SC

29 C NO5 YES YES6 NO7

Marengo® 0.0224G

YES YES NO NO7

benefin + oryzalin XL 2G 3 + 3 C YES YES NO YES

pendimethalin + dimethenamid-p

FreeHand® 1.75G 3 + 15 C YES YES NO YES

trifluralin + isoxaben

Snapshot® 2.5TG 3 + 21 C YES YES NO YES

prodiamine + isoxaben

Gemini™ 3.7SC 3 + 21 C YES YES NO NO

oxadiazon + pendimethalin

Jewel® 3.25G 14 + 3 C YES YES NO YES

oxadiazon + prodiamine

RegalStar® II 14 + 3 C YES YES NO YES

oxyfluorfen + oryzalin

Rout® 3G 14 + 3 C YES YES NO YES

oxyfluorfen + pendimethalin

OH2® 3G 14 + 3 C YES YES NO YES

oxyfluorfen + prodiamine

Biathlon® 2.75G 14 + 3 C YES YES NO YES

oxyfluofen + trifluralin

Granular Herbicide 75 5G

14 + 3 C YES YES NO YES

oxyfluorfen + oxadiazon

Double O™ 3G 14 + 14 C YES YES NO YES

6Biology and Management of oxalis (Oxalis stricta) in Ornamental Crop Production

Common Name (active ingredient)

Example trade name and

formulation

WSSA Herbicide

Group1

Efficacy2 Container production

Field production

Greenhouse or fully enclosed

structures

Landscape

trifluralin + isoxaben + oxyfluorfen

Showcase® 2.5G 3 + 21 + 14 C YES YES NO YES

1Herbicide groups are based according to primary sites of action and can be used to select herbicides that have differing sites of action (Mallory-Smith and Retzinger, 2003) so as to minimize the potential for the development of herbicide resistant weeds. 2P = poor control; S = suppression, C = good control. 3Can only be used in selected conifer and deciduous tree species. Check manufacturer’s label for a complete list of species and recommended application methods. 4Can be applied as a directed application around established woody landscape ornamentals. 5Marengo® 0.622 SC can be used in pot-in-pot container ornamentals as a directed application only. 6Labeled for use on greenhouse floors prior to plant production. Plants can be placed back inside greenhouse 24 hrs after application. 7Indiziflam is also available by the trade name Specticle which can be applied to turf and landscape sites.